Magnetic speed-indicator.



J. K. STEWART.

MAGNETIC SPEED INDICATOR.

APPLIOATION FILED AUG.18, 1911.

Patented Apr. 1, 1913.

UNITED STATES Parana OFFICE.

JOHN K. STEWART, OF CHICAGO, ILLINOIS, ASSIGNOR TO STEWART-WARNER SPEED-OMETER CORPORATION, OF THE STATE OF VIRGINIA.

MAGNETIC SPEED-INDICATOR.

7 Specification of Letters Patent.

Patented Apr. 1,1913.

Application filed August 18, 1911. Serial No. 644,731.

tomatically compensating error due to t em perature changes.

It consists of the features and elements shown and described asindicated in the claims.-

In the drawings: Figure 1 is an axial section of an instrument embodyingthis inven tion. Fig. 2 is a partly sectional front elevation, thesection being made at the line, 2,2, on Fig. 1. Fig. 3 is 'an enlargeddetail View of the automatic compensating device and the parts affectedthereby. Fig. 4 is a face view of the instrument.

The instrument shown in the drawings comprisesa case, 1, in the form ofa cup, and hereinafter referred to as the cup, a rotating magnetcarrier, 2, on which are mounted magnets as hereinafter described, saidcarrier being journaled for rotation upon a post, 3, rigid with thebottom or.

back of the cup at the center thereof, and a biased drag element, 4,which is in the form of an inverted cup made of metal of low electricalresistance, as aluminum or copper, the former being preferable onaccount of its lightness, said drag element being mounted on a spindle,5, which is stepped on the post on which the magnet carrier is mountedfor rotation, and having an additional bearing in a plate, 6, closes thecavity of the cup in which the rotary magnet and biased drag arecontained. The spindle, 5, extends above the said plate, 6, and alsothrough a chamber, 7, which it is convenient to provide above said platefor containing an odometer train, not shown, and thence through a dialplate, 8, which closes said chamber, 7, and forms the visible face ofthe instrument, having upon it a scale graduated for whatever sort ofindication is desired, the instrument shown being specifically designedfor indicating speed of travel of a vehicle to which the instrument maybe attached, the graduation is in terms of miles travel per hour, anindex hand, 10, carried by the spindle traverses the graduated scale- Abiasing spring, 11, attached at one end to the spindle by a collet, 12,and at the other end to a post, 13, projecting from the under side ofthe plate, 6, adjusted for holding the index hand normally at. the zeropoint of the scale when the spring is free from tension. For conveniencethe entire cup and contents, -the parts mentioned,-

are preferably inclosed in a metal shell, 22,

having-. a glass face plate, 23, which covers and protects the dial andindex hand.

The magnet carrier, 2, is made" of non-" magnetic metal and comprises ahub, 2 by means of which it is mounted with ballbearings, 14 -14, on thepost, 3. Concentrio with the bearings, there are mounted rigidly uponthe carrier, 2, two magnets, 15,15, each in the form of a half annulus,or split hollow cylinder, each, however, being slightly less than theentire form of a semi-cylinder, so that when mounted coaxially with thecarrier, the opposed ends of the two magnets are slightly spaced apart.They are positioned with their p les of opposite name, respectively,facing each other, and slightly spaced apart as stated. The attachmentof these magnets to the carrier is rigid so that they revolve therewith.

Positioned within the magnets, 15,15, are two other approximatelysemi-cylindrical magnets, 16,-16, substantially co-axial with the outermagnets and the carrier, and spaced very slightly from the outermagnets, 15, so as to leave a narrow annular space between them, intowhich the inverted cup, or biased drag element, 4, depends and isadapted to oscillate about the axis without contact with the magnets ofeither side.

v The two magnets, 16,-16, are preferably nets a broad quire any pivotalaction. The bi-metallicsateior errors 1 so 7 inside and outside the.depending i which may the outer element,

deflected so as to be cut by the drag positioned with their poles aboutout of line with oles of the outer magnets, 15-15. TlllS position isfound by experiment to produce greater drag upon the biased element thanany other position. The inner magnets are mounted or formed so thattheir poles, or part of them, can be slightly moved toward and from theouter magnets. This is most conveniently accomplished by mounting eachof the magnets, 16, upon the carrier pivotally at one of its poles, sothat the other pole may be swung slightly to move the said other poletoward and from the. outer magnet. For this purpose, as well as'to givethe magbase of support upon the carrier, they are preferably formed,each with an interiorly projecting flange, 16 and a pivotal attachmentof the magnet to the carrier is made by means of a screw, 17 set throughthis flange nearone ole of the magnet into the carrier. For olding theopposite ends of the magnet, 16, and for adjusting ma nets, athermostatic device is provided be in the form of-a bi-metallic, curvedbar, 18, having one end fastened to the 'centralhub of the carrier andthe other end attached to the otherwise free'end the magnet, 16, each ofsaid magnets, 16, being t us provided. In practice, the attachmen't ofthe-thermostatic bar to the magnet may be rigid, the movement being soslight and in such direction as not to rebar has for its inner element ametal having a greater coefiicient ot expansion than crease oftemperature is to straighten or enlargethe curve of saidbi-metallic bar,

the end attached to the magthe latter outward toward at. The slightdistortion from circular orrn which this change causes is negli 'ble. Amovement ota very few thousan the of an inch being suficient to effectall'the'change necessary to compenthereby causin net, 16, .to pus theouter ma F. In this construction, the

ture upto 100 between the outer magnet op osite each ga inner magnets abe cut by-thelatter; and similarly the inher magnet opposite each gapbetween the two outer gnets afiords a path f r the to be flux of saidouter'magnets, causing it element. the means of employing magnets bothflange of the drag element, the same advantage of defleeting the flux ofeach pair so as to be cut by the drag element is obtained as it, in-vthem .toward and from the outer I so that the efiect of in due to achange of temperaords a path or the flux of the inner magnet and causesit to be largely deflected across stead of the other pair, there wereonly a magnetic mass, and in addition there is obtained the advantage ofthe increased magnetic force derived from two pairs of magnets insteadof one pair only.

I claim 1. In a magnetic speedometer in combination with a magnetcarrier mounted for rotation, two sets of magnets 'mounted thereon forrotation therewith, said sets being spaced apart radially to leave aspace of unobstructed clearance between them; a biased drag elementmounted for oscillation about the axis of rotation of the magnet carrierin said clearance space; a cooperating graduated, scale and pointer, onemounted firgedly andathe other carried by the biased drag element, amagnet of one set being mounted so asto have one pole movable toward andfrom the path of the other set, and'ia thermostatic device on thecarrier connected to such movable pole for so moving it,"*-.by change oftemperature of the thermostatic device.

2. Inna magnetic speedometer in combination with a magnet carrlermounted for rotation, two sets'of magnets mounted thereon for rotationtherewith, said sets being spaced apart of clearance between the pathsof rotation;

to leave an unobstructed space a. biased dra element mounted, foroscillation in said 0 earance space, one of the magnets of one set beingmounted on the carrier for movement of one of its poles relatively tothe poles of the other set, and a then mostatic device attached at oneend to the ice carrier and at the other end to said movable magnet,adapted by its expansion and con-' traction to 'move the latter uponchange of temperature.

3. In a magnetic speedometer in combina tion with a magnet carriermounted for rota tion, two pairs of magnets mounted thereon, one withinthe other, the biased drag element mounted for oscillation about theaxis of the magnet and intruding into the spacebetween the paths ofrotation of the two sets, the magnets of the inner set being mov ablymounted on the carrier, and. a bi-metal lic, thermostatic deviceconnecting said no l movable magnets with the carrier for movementtoward and from the axis for movement relatively to the outer magnet'bythe expansion and contraction of said lei-metal 4. In a magneticspeedometer in combina tion with a magnet carrier mounted for iota-n v 3tion, two pairs of magnets mounted thereon i lie device.

therewith, one within the-other;

element mounted ,for oscilla for rotation a biased drag tion about theaxis of rotation ofthe Triag net carrier in the space between the paths,of rotationof the two pairs of magnets.

the magnets of the on the carrier for inner pair being pivoted movementtoward and from the outer magnets and bi-metallic de- In testimonywhereof, I have hereunto set vices attached at one end to the carrierand my hand at Chicago, Illinois, this 12th day at the other end to thepivoted magnets of August, 1911.

adapted to move the latter toward and from JOHN KQSTEWART. the outermagnets by change of form of Witnesses: said thermostatic device uponchange of (hue. S. BURTON,

temperature. EDNA M. MACINTOSH.

